Necessary promotion to bishop from an actual computer game:

[Dann Corbit]

[d]5r2/6P1/8/8/2P5/1P6/2K1p3/4k3 w - - acd 20/30+; acn 4783893; acs 9; bm gxf8=B; ce 32468; pv gxf8=B Kf2;

[Dann Corbit]

Another:
[d]6r1/5P2/8/4KN1k/8/8/8/8 w - - acd 4/4; acn 160; acs 0; bm fxg8=B; ce 32722; pv fxg8=B;

[Dann Corbit]

Another:
[d]6r1/k6P/P3R3/8/6p1/6K1/8/8 w - - acd 17/28; acn 36701781; acs 23; bm hxg8=B; ce 32758; pv hxg8=B Kb8 Re7 Kc8 a7 Kd8 Rb7 Kc8 a8=Q#;

[Dann Corbit]

Another:
[d]8/4R2P/5pk1/5p2/5P2/7K/7N/6q1 w - - acd 19/43; acn 98710030; acs 24; bm h8=B; ce 3; pv h8=B Qf2 Rg7+ Kh5 Rg3 Qxf4 Bxf6 Qh6 Bd4 f4 Rc3 Kg6+ Kg2;

[Dann Corbit]

Another:
[d]8/PQ4pk/5p1p/5P1P/r4PK1/4qB2/4N3/8 w - - acd 19/40; acn 85802882; acs 25; bm a8=B; ce 501; pv a8=B Ra2 Ng3 Qe8 Qe4 Qf8 Bc6 Rb2 Qe8 Qxe8 Bxe8 Kg8 Bd7;

[Uri Blass]

In most of the diagrams there is an alternative win that is not by bishop underpromotion.

You can analyze the position with rybka and only in 2 of them she does not see a clear advantage.

It may be interesting to see the relevant computer game for the following diagrams
[d]5r2/6P1/8/8/2P5/1P6/2K1p3/4k3 w - - 0 1
[d]8/4R2P/5pk1/5p2/5P2/7K/7N/6q1 w - - 0 1

Maybe white could win earlier without a bishop underpromotion and simply prefered to get position when the only way to win is with a bishop underpromotion.

Uri

[sje]

[d]8/PQ4pk/5p1p/5P1P/r4PK1/4qB2/4N3/8 w - - acd 19/40; acn 85802882; acs 25; bm a8=B; ce 501; pv a8=B Ra2 Ng3 Qe8 Qe4 Qf8 Bc6 Rb2 Qe8 Qxe8 Bxe8 Kg8 Bd7;

More subtle than the rest; Symbolic says:

PV: 1. a8=B Ra2 2. Qb5 Qe7 3. Bad5 Rd2 4. Qa6 Qe8 5. Ng3 Rb2 6. Ne4 Qf8 7. Qd6 Qxd6 8. Nxd6 Rd2 9. Nf7 Rb2 Score: +4.068

[glorfindel]

Steven, do you have plans to release Symbolic? I guess it would be an interesting program to play and analyse with.

[Steelman]

OMG! I never thought about the positions you have shown!

I see that my assumption of allowing my program to only promote to a queen or knight is an error! I thought that sometimes a night promotion may sometimes be required so I allow that. But not a bishop or rook.
As a player with my program I allow a promotion to any piece.

Looks like I need to allow a bishop as an under promotion as well. Is there a position which promoting to a rook is required or can I leave the rook out?

[Dann Corbit]

A few more:
[d]6r1/7P/1R6/5k2/8/4R1K1/8/8 w - - acd 20/20; acn 44329606; acs 20; bm hxg8=B; ce 32764; pv hxg8=B;